1. Field of the Invention
A ball valve consists of a valve body defining internally a chamber communicating with the outside through an inlet duct and an outlet duct and accommodating a ball which is pierced by a passage, the ball being rotatable from an open position in which the inlet and outlet ducts are brought into communication with each other to a closed position in which the ball interrupts the communication between the inlet and outlet ducts.
2. Description of Related Art
The use of ball valves to intercept a fluid in a pipe has been known for some time. The characteristic element of these valves is the fluid intercepting member which consists of a ball pierced by a cavity. The ball is movable from an open position, in which this cavity lies in the axis of an inlet pipe and an outlet pipe to permit the passage of a fluid, to a closed position to prevent the passage of the said fluid.
However, it has been observed that, when the ball is moved abruptly from the open position to the closed position, there are sudden pressure fluctuations caused by the movement of the ball (water hammer).
It has also been found that this type of valve, owing to its structure, is not capable of preventing sudden and high pressure increases in the inlet pipe from damaging gaskets and other elements disposed along the said pipe. The pressure increases may be caused, for example, by temperature rises or by rises in the rate of flow of the fluid.
These disadvantages have hitherto prevented a wider application of these valves, as for example in the "sprinkler" type of fire-fighting equipment, where the valves are used to discharge the water from the equipment. This fire-fighting equipment substantially consists of a water distribution network formed by a plurality of pipes. Sprinklers, each of which substantially consists of a nozzle closed by a plug, are disposed along the pipes. This plug consists, for example, of a glass shell filled with a fluid whose volume increases with a rise in temperature. As a result, in the event of fire, the increase in the volume of this fluid causes the plug to fracture and consequently the water can flow out of the pipe through the nozzle.